Iron Nitrate-Mediated Selective Synthesis of 3‑Acyl-1,2,4-oxadiazoles from Alkynes and Nitriles: The Dual Roles of Iron Nitrate

A direct strategy for the selective
synthesis of 3-acyl-1,2,4-oxadiazoles
from alkynes and nitriles has been developed under iron­(III) nitrate-mediated
conditions. The mechanism includes three sequential procedures: iron­(III)
nitrate-mediated nitration of alkynes leads to α-nitroketones,
dehydration of α-nitroketones provides the nitrile oxides, and
1,3-dipolar cycloaddition of nitrile oxides with nitriles produces
3-acyl-1,2,4-oxadiazoles under iron-mediated conditions. Iron­(III)
nitrate plays dual roles in the nitration of alkynes and the activation
of nitriles, while the formation of pyrimidine/isoxazole byproducts
can be efficiently inhibited.